[cobirds] odd incident

On July 13 a friend of mine and I hiked up Young's Gulch in Poudre Canyon.  Our target was observing and photographing Lewis's Woodpeckers feeding cicadas to nestlings at one of two nest trees reported by John Shenot, Doug Swartz, Josh Bruening and maybe others around the 4th of July.  We did NOT see any Lewis's Woodpeckers on the 13th, presumably because at least the lower nest (1.6 miles up the trail) had fledged and the family dispersed.   We did not hike up to the higher nest reported at 2.8 miles up the trail.

On the way back to the car we heard a begging young bird in a ponderosa pine.  With woodpeckers on our mind, I let the power of "want" convince me this was maybe a young Lewis's Woodpecker.  The location was just below the lower of the two Lewis's nest reported on the 4th.  After several minutes of trying to see the beggar in the tree, a bird flew into the pine and fed it.  The bird was an adult female Bullock's Oriole.  After the feeding, the oriole flew off and down into the shrubby understory nearby, which my insect-collecting partner and I knew was rich in food.  After a few more visits to the still-hidden beggar, we had to move on.  After thinking, "I've heard that obnoxious noise before", I am convinced the beggar was a fledged Brown-headed Cowbird. 

Cowbirds are reported to parasitize Bullock's Oriole nests.  Apparently most of these attempts are thwarted by parent orioles recognizing the parasite's eggs, pecking them and throwing them out.  But apparently a few cowbird parasitism attempts are successful.  That appears to be the case here.  In Catherine Ortega's BBA II account for Bullock's Oriole she also states the data from BBA II compared to BBA I suggests Bullock's Orioles are expanding their breeding range a bit higher in elevation.  Young's Gulch is in the 7000' range.  Her account also states they will use ponderosa pine and aspen as nest trees in addition to the more common usage of riparian poplars.  While narrowleaf cottonwoods were within a tenth of a mile of this location, ponderosa pine and aspen (and Douglas-fir) were the dominant trees in the immediate vicinity.

I think what we observed was a fairly unusual event: a Bullock's Oriole that nested in the upper reaches of its breeding range, perhaps in a non-poplar, and that allowed the scheme of cowbirds to succeed when most oriole parasitism doesn't.

Dave Leatherman

Fort Collins